Lock type manhole cover



1954 E. D. HECKMAN LOCK TYPE MANHOLE COVER Filed April 11, 1949 ATTORN BY United States Patent LOCK COVER Earle D. Heckmau, Tacoma, Wash. Application April 11, E49, Serial No. 86 ,624- Claims; (Cl; 94-65) The invention relates to improvements in lock type manhole covers.

There are at present several kinds of lock type manhole covers, but in general these require special mating manhole rings or frames, which frames ordinarily require an internal annular flange extending inwardly from the manhole ring, the locking mechanismof the cover being adapted to be engaged beneath the under side of said inwardly extending flange. In many cities the existing manhole frames or rings have a plain straight cylindrical inner wall Which is not equipped with an inwardly projectin ledge.

Even if a city desired to install lock type manhole covers the expense of replacing existing rings or frames and repairing the pavements would make such a project too expensive to be feasible.

One of the objects of the present invention is accordingly to provide a lock type manhole cover which may be readily installed in existingmanhole rings or frames.

A further object of the invention is to' provide a lock type cover which may be readily slid in place by one man and may be readily removed by any authorized individual while preventing accidental or unauthorized removal.

A further object is to provide a cover which can not be forced out of its frame or ring by pressure from entrapped water in a storm sewer.

A further object of the invention is to provide a cover which cannot be removed except by a person equipped with a suitable tool.

A further object of the invention is to provide a lock type cover which when locked in place will not move back and forth on its seat, but is firmly and rigidly held in one position by a series of symmetrically arranged locking members which engage the sides of the ring or frame and accurately and positively center the cover, thus reducing noise and avoiding wear of the cover on its seat.

A further object is to provide a lock type cover which is easily installed and is automatically locked by gravity operation when the manhole cover is placed on its seat.

A further object of the invention is to provide a simple form of locking means which may be readily applied to existing manhole covers not already equipped with locl'ing means.

Other objects and advantages of the device will be apparent from a consideration of the following detailed description and the accompanying drawings in which are set forth an illustrative embodiment of the invention.

in the drawings:

Fig. l is a top plan view of a manhole cover equipped with my improved locking means;

Pig. 2 is a section on line 22 of Fig. 1 showing the cover locked in place; and

Fig. 3 is a fragmentary section corresponding to Fig. 2 but showing the method of releasing one of the locking cams or sectors to permit removal of the manhole cover from its frame or ring.

Referring to the drawings, A denotes a conventional ring or frame herein shown as having a smooth cylindrical inner surface, and B denotes a lock type manhole cover equipped with the improved locking mechanism which is adapted to engage the smooth interior wall of the ring or frame A.

As shown, the manhole frame member A comprises a cylindrical ring portion the interior of which is smooth, and an outwardly extending flange 11 adapted to rest on a suitable foundation. At the top of the ring 10 there is provided a horizontal annular seat 12 for the manhole In L 2 cover B and an upstanding flange 12', the height of which 18 equal to the manhole cover.

The manhole cover B comprises a disk 13 the periphery of which rests upon the seat 12 of the frame A.

Projecting downwardly from the lower surface of the cover are a plurality of lock carrying brackets 14 herein shown as three in number and symmetrically arranged at angles of 126 to each other and each located intermediate the center 15 of the cover and the periphery 16 thereof. These brackets may be cast integral with the disk 13 where the covers are to be made up initially with the in1- proved locking means, or such brackets may be secured to already existing manhole covers not equipped with locking means by welding or other suitable means. Each bracket is slotted or recessed as at 17 at the lower portion thereof and a locking member 18 is pivoted in each slot or recess l7 by means of a hinge pin 19 which may be retained in place by means of cotter pins or the like 20.

As shown, each of the locking members 18 is provided with a convexly curved cam face 21 adapted for engagement with the inner wall of the ring 10 when the cover is seated. The curvature of the cam face 21 is eccentric to the hinge pin on which the member 18 is mounted, and is preferably serrated so as to provide a firmer engagement with the inner wall of the ring it). As will be noted, the distance from the pivot 19 to the vertical wall of the frame is intermediate the distances between the said pivots and the upper end of the cam face 23 and the lower end thereof, the distance to the upper end being longer and the distwice to the lower end being shorter. Stated in another way, the upper edge 2-6 of each sector comprising the locking members 18 is longer than the lower edge 33 thereof and the distance from the pivot point 1? is intermediate the lengths of these two edges.

As shown, the upper wall 25 of each slot or recess 17 within which the locking member 18 is mounted is angularly inclined and is adapted to engage a portion of the upper inclined edge 26 of the locking cam 18 to provide a limiting stop, which stop while allowing a limited pivoti'ng movement of the locking cam retains said cam at all times in a generally outwardly extending position in which its curved surface 21 will be automatically brought into making engagement with the inner wall of the manhole ring or frame as the cover is seated. As is apparent from Fig. 2 a slight space is provided between the stop 25 and the edge 26 of the cam member when these members are parallel, which spacing permits the locking member to assume angular positions slightly above and below that shown in Fig. 2, as indicated in dotted lines in Fig. 3. It will also be apparent that by reason of the relation between the stop or upper wall portion 25 of the recess 17 and the upper edge 26 of the pivoted cam locking member 18, the cam member as a whole is at all times supported in a generally outwardly extending or substantially horizontal position in which a line drawn through the hinge pin 19 normal to the vertical side wall of the manhole ring will at all times intersect the curved locking face 21 of the cam member whereby engagement of such locking member with a vertical surface is insured.

In operation, the seating of the manhole cover B upon the ring A automatically causes the three symmetrically arranged locking members 18 to lock against the cylindrical side wall of the ring. Pressure a plied to the under side of the cover, as for example by t e pressure of entrapped water when the cover is applied over a storm sewer, only serves to tighten the grip of the locking members. It will further be noted that when the cover is gripped by the symmetrically arranged locking members it will be rigidly retained in position and sliding of the cover upon its seat is prevented, thus avoiding wear on the part of both the seat and cover.

In order to release the cover openings 30 are provided which extend through the cover, one being located adjacent each of the three locking mechanisms. A suitable tool 31 having a hook 32 at the bottom thereof may be inserted through one of the slots, the hook being engaged beneath the lower edge 33 of the locking member 18. On raising the hook the cam is readily released owing to the fact that the curvature of the cam surface 21 is eccentric to the pin 19, as previously indicated.

By means of the three positively operating cam locks -herein disclosed conventional manhole covers can be adapted to lock into existing rings or frames. By properly adjusting the length of the cam looks or the location of the center pin 19 the locking principle may be adapted to manhole rings having an inner projecting ledge for a seat as well as to rings having plain straight cylindrical inner wall as herein disclosed. Both types of rings are in use 1n various cities.

In case of an irregular seat in the ring or on the cover, or in case there is dirt, sand or other foreign material left on the ring seat when the cover is slid into place, which would ordinarily result in a rocking manhole cover, the three symmetrically arranged cam locks of the present invention serve to lock the cover tight. The more vibration the cover is subjected to the tighter the cams grip the ring.

The locking mechanism of the present invention is extremely simple and includes only one moving piece which falls into place through its own weight. By means of separate brackets of suitable design the cam lock idea may be applied to existing covers, the brackets being secured by cap screws, bolts, welding or the like. Thus the present invention may be applied to conventional covers and rings without the expense of replacement of the manhole rings, which are generally set in concrete.

The three locking cams effectively prevent the lid from being removed without first lifting one of the cam locks. When the cover is locked in place wear on the seat between the ring and cover caused by the moving of the lid under heavy traffic is efiectively prevented. The three cam locks prevent the rattle and noise occasioned by trafiic moving over loose manhole covers. Moreover, the improved locking means of the present device will serve to prevent the occurrence of tragic accidents in which persons have been plunged into open storm sewers and drowned or injured thereby. The cam locks will also prevent the covers from being blown into the air during a sewer gas explosion. In addition, the cam lock manhole cover of the present invention will prevent children from removing the covers in outlying districts and filling storm sewers with rocks and debris, which is often the case.

The invention has been described in detail for the purpose of illustration, but it will be obvious that numerous modifications and variations may be resorted to without departing from the spirit of the invention.

I claim:

1. A gravity-locking manhole cover having a fixed lockcarrying lug projecting downwardly from the under side thereof and a locking member loosely pivoted to said lug and projecting outwardly therefrom, and having an outer cam face adapted to lockingly engage a side wall portion of a manhole frame when the cover is upon the frame, the distance between the pivot point and the upper end portion of the cam face being longer than the distance between the pivot point and the lower end portion of the cam face, and fixed stop means carried by said lug for limiting the pivotal movement of said locking member and serving to hold said member normally in laterally disposed wall engaging position.

2. A gravity-locking manhole cover having a fixed bracket secured to the under side thereof and slotted at its lower end, a locking cam member of sector shape loosely pivoted in said slot, stop means carried by said bracket and adapted to engage said locking member to hold the same normally in laterally disposed wall engaging position, the curvature of the cam surface of said locking member being eccentric with reference to the pivot on which the locking member is mounted, the upper edge of said cam member being longer than the lower edge.

3. A self-locking and self-centering manhole cover having a plurality of like symmetrically disposed lugs projecting from the under side thereof, each lug being mounted at a position intermediate the center of the cover and the periphery thereof, gravity-actuated laterally extending sector-shaped locking members carried by the lugs, each locking member being loosely pivoted at one end to a corresponding lug and having a curved cam surface adapted to engage the wall of a manhole frame when the manhole cover is placed thereon, the distance between the pivot point of each locking member and the upper end portion of the cam surface of said member being greater than the distance between the pivot point and the lower end portion of the cam surface, and stop means carried by said lugs for limiting the movement of the locking members and holding them normally in laterally disposed wall-engaging position.

4. In combination with a manhole frame having a depending annular wall, a gravity locking manhole cover adapted to be supported upon said frame, said cover having a plurality of loosely pivoted outwardly extending locking members carried by the under side thereof having cam surfaces engaging the annular wall and serving to center the cover, the distance between the pivot point of each locking member and the upper end portion of the cam surface of said member being greater than the distance between the pivot point and the lower end portion of the cam surface, and stop means carried by the cover and coacting with said locking members for limiting the pivotal movement thereof in either an upward or a downward direction.

5. In combination with a manhole frame having a depending annular wall, a gravity locking manhole cover adapted to be supported upon said frame, said cover having a plurality of loosely pivoted outwardly extending locking members carried by the under side thereof having cam surfaces engaging the annular wall and serving to center the cover, said cam surfaces being serrated, the distance between the pivot point of each locking member and the upper end portion of the cam surface of said member being greater than the distance between the pivot point and the lower end portion of the cam surface, and stop means carried by the cover and coacting with the locking members for limiting the pivotal movement thereof.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 317,153 Lowrie May 5, 1885 416,276 Shuster Dec. 3, 1889 670,335 Tilden et al Mar. 19, 1901 748,394 Martin Dec. 29, 1903 862,746 Martin Aug. 6, 1907 1,171,908 Ware Feb. 15, 1916 1,229,429 Farley June 12, 1917 1,473,986 Brown Nov. 13, 1923 1,560,280 Martin Nov. 3, 1925 1,632,243 Myers June 14, 1927 2,339,455 Britton Jan. 18, 1944 2,436,016 Myers Feb. 16, 1948 FOREIGN PATENTS Number Country Date 3,104 Great Britain Dec. 14, 1864 

